342 



AVES. 



are partially covered by a slight projection of 

 membrane. 



The pulmonary artery divides, almost im- 

 mediately after its origin, into two branches, 

 one to each lung; the ramifications of each 

 artery form plexuses upon the air-cells, and 

 freely anastomose with the pulmonary veins; 

 these leave the lung by a single trunk, and 

 the two pulmonary veins unite into one before 

 terminating in the left auricle. 



The thoracic-abdominal cavity is subdivided 

 and intersected by a number of membranes; 

 the greater part of the cells thus formed are 

 filled with air. The texture of their parietes 

 possesses considerable firmness in the larger 

 birds, as the Ostrich and Cassowary, in which 

 they were described by the French Academi- 

 cians as so many distinct bags. 



The innermost layer of the air-receptacles 

 can be separated from the outer layer, and is a 

 continuation of the lining membrane of the 

 bronchial tube; the outer layer is a serous 

 membrane, and appears to form the cells by a 

 series of reflections of what may be regarded 

 as the pleura or peritoneum. 



These large membranous receptacles into 

 which the extremities of the bronchial tubes 

 open are disposed with sufficient general regu- 

 larity to admit of a definite description and 

 nomenclature. 



Fig. 173. 



Air-receptacles of a Swan. 



The first or inter-clavicular air-cell (, 

 173) extends from the anterior part of ea< 

 lung, forwards to the interspace of the fur- 

 culum, anterior to which it dilates in the 

 Gannet and many other birds into a large 

 globular receptacle. In the Vultures it is di- 

 vided into two lateral receptacles, between 

 which the large crop is situated. A thin fan- 

 shaped muscle is extended from the anterior 

 edge of the furculum, over the interclavicular 

 air-cell in these and some other birds 



The anterior thoracic cell (6) contains the 

 lower larynx and bronchi, and the great vessels 

 with their primary branches to the head and 

 wings. It is traversed by numerous mem- 

 branous septa, which connect the different 

 vessels together, and maintain them in their 

 situations. The air passes into the posterior 

 part of this receptacle by two openings at the 

 anterior part of the lungs. The deep-seated 

 air-cells of the neck are continued from it 

 anteriorly. 



The lateral thoracic cells (d) are continued on 

 each side from a foramen on the inner edge of 

 the lung, situated just opposite the base of the 

 heart ; they are covered by the anterior tho- 

 racic air-cell, and from them the air passes 

 into the axillary and subscapular cells, into 

 those of the wing, and into the humerus (e). 

 They also communicate with the cellula cordis 

 posterior (c), behind the heart and bronchi, 

 which cell is often subdivided into several 

 small ones. 



The cellula hepatica are of much larger 

 size ; they are two in number, of a pyramidal 

 figure, with their bases applied to the lateral 

 thoracic cells, and their apices reaching to the 

 pelvis : they cover the lower portions of the 

 lungs and the lobes of the liver ; they receive 

 air from several foramina situated near and at 

 the external edge of the lungs. 



The cellula abdominales commence be- 

 neath the cellulse hepaticae at the inferior ex- 

 tremity of the lungs, where the longest branches 

 of the bronchiae open freely into them. (A 

 bristle is passed through one of these openings 

 in the figure.) They are distinguished into 

 right (f) and left (h) ; the former is gene- 

 rally the largest receptacle in the body ; it ex- 

 tends from the last ribs to the anus, and covers 

 the greater part of the small intestines, the 

 supra-renal gland, and kidney of the same 

 side. The left abdominal cell (A) contains the 

 intestines of its own side, and is attached to 

 the gizzard. In some large Birds, as the 

 Gannet, it is separated from the right recep- 

 tacle by a mediastinal membrane (g) which is 

 continued from the gizzard to the anus. 



Both the abdominal receptacles transmit 

 air to the pelvic cells (i, k) of their respec- 

 tive sides, and to several small and extremely 

 delicate cells between and behind the coils of 

 intestine. One of these is continued round the 

 fold of the duodenum and pancreas to the 

 gizzard, and has been termed the duodenal 

 cell. 



From the inguinal cell are continued the in- 

 termuscular glut&al and femoral cells, which 

 surround the head of the femur, and commu- 

 cate with that bone by an aperture (1} situated 



