A doubling back of the tendon of the short alar extensor on to the nodule of origin of the long radial extensor of the carpus has been shown by Professor Garrod to be characteristic of the true Passeres. See P. Z. S. 1876, p. 509; Prof. Bell's translation of Muller's Vocal Organs of the Pas-seres, Appendix by Garrod, p. 64, Oxford, 1878.
2 This muscle corresponds with No. 19, the Deltoides externus of Schoepss, as given in his monograph on the Muscles of Flight in Birds in Meckel's Archiv for 1829, and is called 'levator humeri' by Tiedemann, and 'le petit releveur de l'humerus' by Vicq d'Azyr. It appears to have been often confounded with the muscle next to be spoken of and lying close to it, which, though similar in function and size, is differently innervated and quite separate from it. The latter muscle is correctly described by Schoepss, I.c. p. 122, and named (No. 20) 'Deltoides inferior.'
The crop forms a sac with bilateral glandular1 pouches at the lower end of the distended oesophagus. As in the oesophagus of all Sauropsida, the muscular coat may be seen to consist of two layers, the outer one of which lies transversely2, and the inner one parallel to the long axis of the digestive tube, whilst both alike consist of unstriped fibres, and thus contrast in two points with the muscular coat of both Mammals and Fishes. It rests on either side upon the furcula and the muscles arising from it. In the cavity of the thorax a black bristle has been passed between the proventriculus and the aorta as this vessel arches over from the left to the right. The right side of the heart rests upon the right lobe of the liver from which the vena cava inferior is seen to pass up into the right auricle, entering it at a point a little superiorly as well as posteriorly placed to that at which the vena cava superior of the right side opens into it. The left lobe of the liver is, like the right, deeply excavated on its inner aspect for the reception of the heart; and it is still more extensively excavated on its under surface for the reception of the powerful gizzard, so as to be less than one-half the size of the other main lobe of the gland.
The veins from the upper extremity and shoulder are cut short at their point of junction with the jugular to form the vena cava superior. The pneumogastric nerve is seen in relation superiorly with the jugular vein; superiorly again, and internally to the nerve, we see the proventriculus; and superiorly again to it, the longi colli muscles arising from the vertebral hypapophyses. Tracing the aorta backwards towards the heart from the point where it arched over the right bronchus, which, together with the pulmonary artery placed before it and the pulmonary vein placed behind it, has been removed in this dissection, we see it pass behind the vena cava superior dextra, and give off the two arteriae innominatae, one for either side of the body, very close to the base of the heart. These two arteries together with the pulmonary artery give a characteristic appearance to the region at the base of the heart in all Birds. Each arteria innominata divides into a common carotid3 and a subclavian trunk. The subclavian, after giving off a small branch homologous with the internal mammary artery of anthropotomy, divides into an axillary trunk, which passes into the wing together with the brachial nerves, and into the much larger arteria thoracica externa which supplies the great pectoral muscles.
The gizzard is concealed from view by the right lobe of the liver and the posterior or xiphisternal end of the sternum which supports and protects both these viscera. The duodenal loop containing the pancreas, and the segment beyond that portion readily recognisable as belonging to the duodenum by its large calibre, form a rudimentary spiral coil. The distal end of the loop and of the pancreas inside it are bent upon the proximal segment next to the gizzard, and are in relation with the lower lobe of the kidney on the right as the gizzard is with the lower lobe of the kidney on the left side. The distal segment of the duodenum bends up at some distance from its pancreatic loop and comes into relation with the right lobe of the liver which is excavated to receive it. In the interval between these coils of the duodenum portions of the two other convolutions characteristic of Columbae show themselves. Of these the distal one is the smaller in calibre; it shows some Peyerian glands, and is connected with the proximal portion of the duodenum by a lamina of mesentery much as is the colon in the Rabbit (see Fig. 2, supra). The coil interposed between the duodenal and the distal coil is much the longest and most distinctively spiral of the three, but being placed dorsally to them is not seen in its full extent till they are displaced1. The lung, which occupies a much smaller space in the dorso-sternal plane than in mammals, and in an ordinary dissection of a bird's viscera scarcely comes into view until either the ribs are displaced a little outwards or the lobes of the liver a little inwards, reaches backwards so far as to interpose itself for some distance between the anterior lobe of the kidney and the -os ilii.
Anteriorly one of the musculo-tendinous languettes which in the Bird represent the diaphragm of mammals passes inwards from the rib to the covering of the lung and interposes itself between the region of the anterior kidney-lobe and that of the lung. The Bird's differs further from the Mammalian lung in being lodged conformably to the intercostal spaces, and being indented by the six unanchylosed ribs, instead of being freely suspended, as is invariably the case in mammals, and divided into lobes, as is very ordinarily the case in those animals2. Another and most important point of difference is furnished by the prolongation of the lung, by means of its bronchial stem and branches, into air-cells permeating a very large part of the entire body. The largest of these receptacles are the infra-renally placed 'abdominal air-sacs,' the right one of which extends from the posterior border of the lung above and behind the liver, so as, firstly, to interpose itself between the inferior surface of the kidney and the intestines, and, secondly, to stretch beyond the region of the kidney into that of the rectum.