ANATOMY OF A BIRD. 245 



midriff, are ordinarily said to be absent in birds, and, indeed, in most cases are but feebly represented. 

 In the Ratitre, and especially in the New Zealand form (Apteryx) of this group, the diaphragm 

 may attain to a very fair degree of completeness, though even here the apex of the heart is 

 allowed to pass into the abdominal cavity. The muscles of the back are feebly developed, as might 

 be imagined from the firm character of the spinal column ; and as the fore limb exhibits but slight 

 power of varying its movements, its muscles are not well developed. Those muscles which are found in 

 the skin are, on the contrary, expanded into broad pieces ; and special bundles are sent to the larger 

 feathers of the wings and of the tail, and to those folds of skin which connect the upper arm with the 

 trunk, and with the fore arm, respectively. Borelli thus explains the arrangement by which a 

 perching bird remains fixed when asleep : A muscle which arises from the pubes bone of the hip- 

 girdle passes over the knee, and then takes a backward direction so as to pass behind the ankle ; it 

 thus becomes one of the flexor muscles, by the contraction of which the toes are flexed, or bent. 

 When the perching bird, which, as we know, has one of its toes directed backwards, is seated on a 

 bough, the thigh has its upper end directed backwards, while the upper joint of the leg is turned for- 

 wards, or in other words, the two parts of the leg have opposite directions. This arrangement acts 

 as a contracting influence on this muscle and its tendons, while the weight of the bird is sufficient to 

 preserve this condition and the consequent flexion of the toes. 



To turn to those muscles the arrangement of which hap been made the basis of a suggested classi- 

 fication. In the leg of the bird there are, among others, four muscles, the names of which &refemoro- 

 caudal, accessory femoro-caudal, semi-tendinosus, and accessory semi-tendinosus, any of which may be 

 absent, but in those cases where a single muscle only is found the first is always present; again, there 

 is a muscle which, from its course, is known as the ambiens, and this, too, may be present or may 

 be absent. As the presence or absence of any of these muscles is a very constant phenomenon 

 in any given section of birds, it has been proposed to divide the class into those which do, and 

 those which do not, possess the above-named ambiens muscle. In the latter group the second of the 

 four above-named muscles the accessory femoro-caudal is never present. * 



Of all the muscles, those which act in aid of the vocal organs are of the greatest interest, 

 but they will be considered a little later on. 



A valuable suggestion has been made, which, if followed out, may lead us to understand 

 how it is that the brain of the bird, which is so simple as compared with that of man, is 

 nevertheless capable of so much intelligent activity. Bearing in mind the axiom that it is quality 

 not quantity that tells, and looking at the fact that the brain of the most highly intelligent 

 man is, after death, supposed to be similar to that of the foolish and of the unwise of our 

 race, it is obvious that the essential difference must lie elsewhere than in the coarser, or more 

 evident, characters of that organ which is known as the brain. The suggestion, then, that was made, 

 was to the effect, that the possessors of aviaries, in which it was possible to study the characters of 

 birds, should submit the brains of their deceased favourites to that more thorough investigation which 

 the microscope allows of. The brains of birds vary but little in their anatomy. The optic lobes are 

 rounded, paired, and tubercular in the bird, and are not divided into four, as in mammals ; they 

 are found at the lower part and sides, and not in the upper part of the brain. The cerebellum is not 

 continued at the sides into distinct lobes ; nor are the two lobea of the brain (or cerebral hetnispJieres] 



* The presence or absence of it, or of the other muscles, is used as a means for arranging the smaller divisions of the 

 larger groups into which the two first-named sub-classes are, by the aid of other anatomical facts, divided. One striking 

 advantage of this system, as suggested by the late Prof. A. H. Garrod, is that the characters of the airibitns have been 

 observed to go hand in hand with certain other characters. Thus, the caeca found at the end of the small intestine are 

 always present in the Homalogonatae, or birds having the normal arrangement of knee-muscles ; but in this connection there is 

 another structure to be mentioned, namely, the so-called oil-gland, or gland by the secretion of which the bird "preens" its 

 feathers, and which is always set in the skin in the region of the tail. Now this " uropygial," or oil-gland, may or may not be 

 provided with a tuft of feathers, and as there may or may not be cseca to the intestine, it follows that (1) the gland may be 

 tufted and there may be cseca, or (2) the gland may have no feathers and caeca may be present, or (3) there may be no cseca 

 and a tufted gland, or (4) there may be no caeca and no tufts (the possible arrangement of neither being present is found in a 

 few Pigeons). But this is not the place to follow out the details of this classification. 



With regard to the proposition made by a French observer, M. Alix, that birds should be divided into the Homoco- 

 myarii, Entomyarii, and Ectomyarii, according to the character of certain of the flexor muscles at the back of the leg, it 

 seems only necessary to remark that so far anatomical investigations have not supported his views, while his system would 

 separate birds which seem to be closely allied. 

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