636 



ANATOMY OF VERTEBKATES. 



44G 



symmetrical pair of longish simple sacs, extending from the 

 pharynx on each side of the oesophagus to the beginning of the 

 liver : the left division soon begins to exceed the right in length, 

 and then seems to monopolise the power of growth. The common 

 stem or neck of the pulmonary sacs elongates, contracts, and 

 begins to show traces of the transverse cartilages ; and at about 

 the latter third of the developemental period the right lung appears 

 as a mere appendage to the beginning of the left. The appear- 

 ance of malpighian bodies, as minute red points on part of the 

 surface of the primordial kidneys, is the first indication of the 

 developement therefrom of the kidneys : these grow between 

 the primordial kidneys and the vertebra at the hindmost end of 

 the abdominal cavity. The testis, or ovary, is differentiated from 

 the ventral surface of the fore-part of the primordial glands : at 



one period of developement the primor- 

 dial ducts coexist with the sperm-duct 

 and ureters. Four or five ducts emerge 

 from the liver and unite into a com- 

 mon one before communicating with 

 the intestine ; a similar duct, proceed- 

 ing from the common one, expands at 

 its opposite end into the gall-bladder. 

 This remains near the pylorus : the 

 hepatic ducts elongate as the intestine 

 recedes on the growth of the snake. 

 The spleen first appears as an append- 

 age to the narrow end of the pancreas. 

 In the male embryo, the two bifurcate 

 penes project from the cloaca before 

 the period of extrication. 



Figure 446 shows the posterior half 

 of the embryo of the Viper at a late 

 period of developement. The yolk 

 bag, , is much reduced in size, but 

 is not yet taken into the abdominal 

 cavity ; b is the portion of the amnios 

 adherent to the vitellicle ; c is the 

 short pedicle, including part of d, the 



ductus vitello-intestinalis, which as- 

 cends to terminate at e, between the 



Foetus of Viper, xi.nr. 



longitudinal lolds 01 the mucous mem- 



G 



brane of the small intestine, f. The continuation of the intestine to 

 the cloaca, /, is shown at y, li ; the ovaria at i, i ; the kidneys at k, ft. 



