The Development of the Frog 73 



up into a series of nine vertebra, followed by a posterior 

 unsegmented portion, which later becomes the urostyle. 

 This transverse division does not affect the notochord, 

 which remains as a continuous structure until the 

 complete absorption of the tail at the end of the met- 

 amorphosis. Shortly after the metamorphosis thin rings 



FIG. 27. DIAGRAMMATIC FIGURE OF THE ARTERIAL SYSTEM OF 



THE MALE FROG, FROM THE RIGHT SIDE. (After Marshall.) 



a, stomach. b, nostril, c, small intestine, c a, carotid artery. eg; 

 carotid gland, c m, coeliaco-mesenteric artery, en, cutaneous artery. </, large 

 intestine, d a, dorsal aorta, f, femur. A, spleen, ha, hepatic artery. /. 

 right lung, /a, lingual artery. /, testis. o, kidney. oa, occipito-vertebral 

 artery, pa, pulmonary artery, r, pelvic girdle, s, sternum, sa, subclavian 

 artery, sc, sciatic artery, t, tongue, ta, truncus arteriosus. ua, urino- 

 genital arteries, v, ventricle. 1, carotid arch. 2, systemic arch. 3, pulmo- 

 cutaneous arch. 



of bone, slightly constricted in their centres, so as 

 to be hourglass-shaped in section, are developed in the 

 membrane investing the cartilaginous sheath of the 

 notochord : these correspond with the nine vertebrae 

 already present, and form the first rudiments of the 

 vertebral centra. In the intervertebral regions, between 

 the successive bony rings, annular thickenings of the 



