this is to mass the fleshy and heavy parts of the muscle about the centre of gravity of the body, a desideratum for a flying animal. This peculiarity of the muscular system is especially well seen in the muscles of the leg. The muscular system of birds is remarkably constant for the species, the number of variations being apparently, comparatively speaking, but slight. It is true that in but few cases has a large number of individuals been carefully dissected; but of a good many species, on the other hand, have three, four, or even more individuals been dissected from the point of view of the relations or presence of a particular muscle or muscles. The muscular system too is apt to be very constant for a given genus or even a larger division. A glance at the systematic part of this work will show how trifling are the variations even between families in some cases. All these facts lead to the inference that the muscular system in birds is of very considerable value for classificatory purposes. GARROD, FORBES, and FÜRBRINGER are the three anatomists who have laid greatest weight upon the muscular system as an index of affinity. It is, thinks Professor FÜRBRINGER, the muscles of the anterior extremity which have the greatest value of any part of the muscular system. The wing is an organ which is used in much the same way by all birds in which it is properly developed. On the other hand the uses of the muscles of the leg are manifold; we have hopping birds, climbing birds, perching birds, swimming birds, &c. &c. Nevertheless GADOW is inclined to think (with GARROD) that they are the most important. The existing knowledge of the muscles of birds is mainly confined to the muscles of the leg and of the fore limb, a knowledge which we owe almost entirely to GARROD and FÜRBRINGER, many other anatomists having, of course, filled up many details. Less is known about the muscles of the head, neck, trunk, and hyoid region.

It is curious, indeed, how very few birds have been at all thoroughly dissected. Apart from the detailed account of Apteryx by Sir RICHARD OWEN, and of less comprehensive memoirs by COUES on the diver, by MORRISON WATSON

on the penguin, we have only two recent memoirs which contain anything like a complete account of the muscular structure of a given type. These are the book upon Corvus corax by SHUFELDT and a paper by CHALMERS MITCHELL and myself upon Palamedea. The most comprehensive general account of bird muscles is unquestionably that of GADOW in Bronn's Thierreich.' I shall base the following account of avian musculature largely upon the last-mentioned work, adding to it only such details as were inaccessible to GADOW at the time of its publication. The muscles known to vary will naturally be treated at greater length than those of whose comparative structure but little is registered. GADOW allows altogether 112 separate muscles and sets of muscles like those of the ribs, arranged in a serially homologous row. Some of these are, however, divided again. Of these, so far as we know at present, the following are of the greatest systematic importance, as presenting really considerable variations even to disappearance :-Gluteus maximus, gl. anterior.

Obturator internus.

Femorocaudal and accessory femorocaudal.
Ambiens.

Semitendinosus and accessory semitendinosus.
Biceps femoris.

Semimembranosus.

Flexores profundi hallucis et digitorum.
Peronei.

Tibialis anticus.

Pectoralis primus, p. secundus.

Deltoid.

Patagialis.

Biceps.

Anconæus.

Expansor secundariorum.

Cucullaris propatagialis.

The value of muscles in classification has been highly rated by many ornithologists, especially, of course, by GARROD, FORBES, and FÜRBRINGER. It is, however, only a comparatively small number

of the total series of muscles in the body that can be trusted much as evidence of affinity. The ambiens is unquestionably of value as it is found or not found, as the case may be, through whole groups whose mode of progression when walking or climbing is as different as can be. Its total absence from all picarian and passerine birds is a fact upon which I comment elsewhere. There are very few groups in which the ambiens may be present or absent, and in those cases it is often reasonable to separate as distinct families the genera which have it from those which have it not. This cannot, perhaps, be done in every case. Some storks, such as Abdimia, have no ambiens, while the majority have it. There are auks with and auks without this muscle. The same may be said of petrels, parrots, and pigeons. Rhynchops, the only larine bird without an ambiens, may be, perhaps, rightly elevated to the distinction of a separate family. These examples, however, are so few that they may be compared to such singular exceptions as the absence of the odontophore in the nudibranch Doriopsis, which does not in the opinion of any one invalidate the great importance of that structure in arranging the mollusca. In estimating the value of the ambiens the facts of its total or apparently partial suppression, referred to below, must be borne in mind. The entire absence of all trace of the muscle in the owls shows that they are not necessarily to be placed in the neighbourhood of the parrots, in which the muscle, when absent, has left traces behind.

Muscles of the Fore Limb

Pectoralis Primus.-This muscle consists of two parts, the thoracic part, arising from the sternum, and an abdominal portion, arising from the pelvis. The latter portion, well developed in lower vertebrates, is slight in birds, and is often completely absent. The pectoralis thoracicus arises from the sternum, the clavicles, and intermediate membranes ; it is inserted on to the humerus. In ratite birds there is no origin from clavicles, but, on the other hand, an origin from coracoids not present in carinates. There is frequently an intimate connection between the pectoral near its insertion and the tendon of origin of biceps. The pectoralis is frequently divided into two portions, the mode of division being twofold. In Apteryx the coracoidal portion is separate from the sternal, a state of affairs which recalls some of the lower vertebrates;

in others the pectoral is divided into a superficial and deeper layer. In many Ciconiiformes' this is the case. The pectoral, in all birds except the ratites, gives off one or two branches to the patagium. The branch has been termed the pectoralis propatagialis. There are either two separate muscles split off from the surface of the pectoral (as in Nisus), the tendon of one going to the tendon of the tensor patagii longus, that of the other to the tensor patagii brevis; or (Podargus) there is but one muscle which divides into two tendons; or the origins of the two tendons are separate, one of them commencing with a special muscle, the other arising as a tendon from the surface of the pectoralis; or both may be tendinous in origin. Finally, there is in tinamous and gallinaceous birds (some) a special propatagialis posticus,' joining with its tendon that of the other muscle. The pectoralis abdominalis, totally absent in nearly all ratites, in storks, various hawks, &c., is divisible into two parts, of which one or other is sometimes wanting. The pars posterior springs from the pelvis and adjacent fasciæ; it ends in front freely or comes into more or less close relations with the pars anterior. In Anseres, for example, the two form one continuous band of muscle, their boundaries being simply marked by a slight tendinous inscription. The pars anterior arises from the skin close to the termination of the last, or is, as already mentioned, continuous with it; it generally ends upon the humerus, near or in common with the insertion of the main part of the pectoral. In a few birds (quite remote from each other in the system, Pelecanus, Chauna, Cathartes) the terminal tendon is lost in the axillary region; a more remarkable modification, possibly of classificatory importance, is described later in Crypturus. In a variety of birds there is a slip from this muscle to the metapatagium.

Latissimus Dorsi.-This muscle is divided by FÜRBRINGER into three sections

(1) L. d. anterior.

(2) L. d. posterior.

(3) L. d. metapatagialis and dorso-cutaneus.

The first-named muscle is totally wanting in Apteryx and

Alcedo bengalensis. It arises in other birds from the spinal processes of a varying number of cervical and dorsal vertebræ. The narrowest area of origin is seen in Alcedo, Macrochires, and various passerines, where it embraces at most a single vertebra. In other birds it may arise from as many as four and a half vertebræ. The broad fleshy or tendinous, or partly fleshy and partly tendinous, insertion varies in width.

The second division is entirely wanting in Otis, Pterocles, many passerines, &c. It arises from the spinous processes of posterior dorsal vertebræ, ilium, and even adjacent ribs. Its origin is usually widely separated from that of anterior; but there are various intermediate conditions which culminate in the cuckoos, Macrochires, and some other birds, where the two muscles form one, with, however (save in Cypselus), separate insertions. The insertion of this muscle is by a slender tendon in front of that of the latissimus dorsi anterior.

The latissimi dorsi metapatagialis and dorso-cutaneus are two slips running to the metapatagium and the neck region of the skin respectively. They are not often both present, but are in Apteryx, Charadridæ, Alcidæ, and some gallinaceous birds. They are both absent in ratites (excl. Apteryr), Macrochires, Colii, Bucerotidæ, &c. The dorsocutaneus is the rarest, and apart from the instances mentioned is found only in the Cracidæ, piciform birds, and passerines.

Cucullaris.--This is an extensive muscle occupying the greater part of the neck. The only muscle superficial to it is the sphinctor colli. It has two main divisions. The pars cranialis arises from the region of the occipital and the squamosal; in many birds (of the most diverse orders) a branch is given off from this (the dorso-cutaneus), which ends on the back below the spinal pterylon, whose feathers it raises. The main part of the muscle ends upon the clavicle, or sternum, or ligaments in the neighbourhood. In some birds a part of the fibres end upon the fascia covering the pectoralis primus, and in those with a crop some of the deeper fibres come into relation with that Not in 4. ispida.