AVES. 



341 



contribute to the secretory vessels of the liver, 

 but proceed to the superior part of that viscus, 

 to terminate in the vena cava, as does also the 

 umbilical vein. 



" The vein which returns the blood of the 

 inferior extremities is divided in the pelvis 

 into two branches, which correspond with the 

 femoral and ischiadic arteries ; the one passes 

 through the ischiadic foramen, and the other 

 through the hole upo/i the anterior margin of 

 the pelvis; but the proportion they bear to 

 each other in magnitude is the very reverse of 

 what occurs in the arteries ; for the anterior 

 vein is the principal one, whilst the other is 

 not a very considerable vessel, and receives its 

 supply of blood from the muscles at the pos- 

 terior part of the joint. 



' Thefemoral vein (a a), immediately without 

 the pelvis, gives branches on both sides, which 

 receive the blood of the extensor and adductor 

 muscles at their superior part : the trunk passes 

 obliquely under the accessory muscle of the 

 flexor digitorum, and over the os femoris, 

 where it liessuperficially ; it then winds under the 

 adductor muscles, and gets into the ham (b />), 

 where it receives many muscular branches, 

 and comes into company with the artery and 

 nerve. It here divides into the tibial (c c) and 

 peroneal veins. The first is joined by some 

 branches from the surface of the joint answer- 

 ing to the articular arteries; it also receives the 

 anterior tibial vein which accompanies the 

 artery of the same name. The tibial vein pro- 

 ceeds down the leg along with the artery on 

 the inside of the deep-seated flexors of the 

 heel : it turns over the fore part of the articu- 

 lation of the tibia with the metatarsal bone, 

 in order to get upon the inner side of the me- 

 tatarsus; above the origin of the pollex, it 

 receives a communicating branch from the 

 peroneal vein, and immediately after two 

 branches from the toes : one of them comes 

 from the inside of the internal toe ; the other 

 arises from the inside of the external and mid- 

 dle toes, unites at the root of the toes in the 

 sole of the foot, and is joined by a branch from 

 the pollex, before its termination in the internal 

 vein of the metatarsus. 



" The peroneal vein derives its principal 

 branches along with those of the peroneal 

 artery, from the muscles on the outside of the 

 leg. The trunk of the vein comes out from 

 the peroneal muscles, and passes superficially 

 over the joint at the heel, and along the outside 

 of the metatarsus ; near the pollex, or great toe, 

 it sends a branch round the back of the leg, 

 to communicate with the tibial vein ; after 

 which it is continued upon the outside of the 

 external toe to the extremity, receiving anas- 

 tomosing branches from the tibial vein. 



" Where the veins run superficially upon the 

 upper and lower extremities, they seem to 

 supply the place of the branches of the cepha- 

 lic, basilic, and the two sapheruc; but the 

 analogy is lost upon the upper arm and thigh, 

 these branches forming deep-seated trunks; 

 this constitutes the greatest peculiarity in the 

 distribution of the veins in the extremities of 

 birds." 



Respiratory organs, In the course of this 



article we have frequently had occasion to allude 

 to the extent and activity of the respiratory func- 

 tion in the Class of Birds ;* nevertheless the 

 organs subservient to this function manifest 

 more of the peculiarities of the Reptilian than 

 of the Mammalian type of formation. 



The lungs are confined, as in the Tortoise, 

 to the back part of the thoracic-abdominal 

 cavity, being firmly attached to the ribs and 

 their interspaces ; and, as in the Serpent, they 

 communicate with large membranous cells 

 which extend into the abdomen and serve as 

 reservoirs of air. 



In those aquatic Birds, which are deprived 

 of the power of flight, as the Penguins, the air 

 receptacles are confined to the abdomen ; but 

 in the rest of the class they extend along the 

 sides of the neck, and, escaping at the chest and- 

 pelvis, accompany the muscles of the extre- 

 mities. They also penetrate the medullary 

 cavities and diploe of the bones, extending in 

 different species through different proportions of 

 the osseous system, until in some birds, as 

 the Horn-bill, every bone of the skeleton is 

 permeated by air. 



There is, indeed, no class of Animals which 

 are so thoroughly penetrated by the me- 

 dium in which they live and move as that of 

 Birds. Fig. 172. 



The lungs (w, Jig. 172) 

 are two in number, of a 

 lengthened, flattenedjOval 

 shape, extending along 

 each side of the spine 

 from the second dorsal 

 vertebra to the kidneys, 

 and laterally to the junc- 

 tion of the vertebral with 

 the sternal ribs. They 

 are not suspended freely 

 as in Mammalia, but are I 

 confined to the back part j 

 of the chest by cellular] 

 membrane,and the pleura 

 is reflected over the sternal 

 surface only, to which the 

 strong aponeurosis of the 

 diaphragmatic muscles is 

 attached. They are con- 

 sequently smooth and 

 even on the anterior R*9 ht lun ff f a 

 surface, but posteriorly are accurately moulded to 

 the inequalities of the ribs and intercostal spaces. 



The lungs in general are of a bright red 

 colour, and of a loose spongy texture. The 

 bronchi (u,Jig. 163; a, Jig. 172) penetrate their 

 mesial and anterior surfaces about one-third 

 from the upper extremities; they divide into 

 four, five, or six branches, which diverge as 

 they run along the anterior surface ; some in- 

 complete cartilaginous rings are found through 

 their entire extent. 



The orifices of the air-cells of the lungs (c c, 

 fig. 172) open upon the posterior parietes of 

 the bronchial tubes, while the extremities of 

 these tubes terminate by wide openings (b b, 

 Jig. 172) in the thoracic and abdominal air- 

 receptacles. These orifices are oblique, and 



* .According to Lavoisier, two Sparrows consume 

 as much oxygen in a given time as ouc Guinea-pig. 



