HYPOPHYSIS CEREBRI. 



157 



Coccygeal and Carotid Glands. The former, which lies on the tip of the coccyx, is composed 

 to a large extent of plexuses of small, more or less cavernous, arteries, supported and enclosed 

 by septa and a capsule of connective-tissue (Luschka). Between these lie polyhedral granular 

 cells arranged in networks. The carotid gland has a similar, structure (p. 77). Their functions 

 are quite unknown. Perhaps both organs may be regarded as the remains of embryonal blood- 

 vessels (Arnold). 



104- COMPABATIVE. The heart in fishes (fig. 129, I.), as well as in the larvse of amphi- 

 bians with gills, is a simple venous heart, consisting of an auricle and a ventricle. The 

 ventricle propels the blood to the gills, where it is oxygenated (arterialised) ; 

 thence it passes into the aorta to be distributed to all parts of the body, and 

 returns through the capillaries of the body and the veins to the heart. The 

 amphibians (frogs) have two auricles and one ventricle (Frog, II.). From 

 the latter there proceeds one vessel which gives off the pulmonary arteries, 

 and as the aorta supplies the rest of the body with blood, the veins of the 

 I iy 1 systemic circulation carry their blood to the right auricle, those of the lung 

 into the left auricle. In fishes and amphibians there is a dilatation at the 



Fig. 129. 



Schemata of the circulation. I. Fish. A, auricle ; S, sinus venosus ; V, ventricle ; B, bulbus 

 aortse ; c, branchial arteries ; i, branchial vessels ; Vv, branchial veins ; is^circulus cephali- 

 cus aortas ; F, common aorta ; G, caudal artery ; If, duct of Cuvier ; 7, anterior, and K, 

 posterior cardinal veins ; L, caudal vein ; M, M, kidneys. II. Frog. I, sinus venosus ; II, 

 and III, right and left auricles ; IV, ventricle ; V, aorta with the bulb ; 1, pulmonary 

 arteries ; 2, arch of the aorta ; 3, carotid ; 4, lingual ; 5, carotid gland, and 6, axillary 

 arteries ; 7, common aorta ; 8, cceliac artery ; 9, cutaneous artery ; Vv, pulmonary veins ; 

 p, p, lungs. III. Saurians. I, right auricle, with the vena? cava? ; II,-right ventricle ; 

 III, left auricle ; IV, left ventricle ; V, anterior common aorta ; 1, pulmonary artery ; 

 2, arch of the aorta ; 3, carotid artery ; 4, posterior common aorta ; 5, cceliac, and 6, 

 subclavian, arteries ; 7, pulmonary veins ; 8, lungs. IV. Tortoise. I, right auricle with 

 the vena? cavse ; II, right, and IV, left ventricles ; III, left auricle ; 1 and 2, right 

 and left aorta? ; 3, posterior common aorta ; 4, cceliac, 5, subclavian, 6, carotid, and 7, 

 pulmonary arteries ; 8, pulmonary veins. 



commencement of the aorta, the bulbus arteriosus, which is partly provided with strong muscles. 

 The reptiles (III.) possess two separate auricles, and two imperfectly separated ventricles. 

 The aorta and pulmonary artery arise separately from the two latter chambers. The venous 

 blood of the systemic and pulmonary circulations flows separately into the right and left auricles, 

 and the two streams are mixed in the ventricle. In some reptiles the opening in the ventricular 

 septum seems capable of being closed. The complete separation of the ventricle into two is 

 seen in fig. IV., in the tortoise. The lower vertebrates have valves at the orifices of the venae 

 cavae, which are rudimentary in birds and some mammals. All birds and mammals have two 



