The Frog 73 



suppose that different end-organs in the skin of the frog may also have 

 definite functions. 



THE SKELETON 



The frog is possessed of an endoskeleton as is man. The bones and 

 cartilages constituting this endoskeleton furnish a support which holds 

 the muscles and organs of the body in position. 



For convenience sake the skeleton is divided into two parts, the 

 axial portion (Fig. 20), comprising skull and vertebral column, and the 

 appendicular portion (Figs. 21, 22), consisting of the pectoral or shoul- 

 der, and pelvic or hip girdles, together with the bones of the limbs which 

 these girdles support. 



The frog's skeleton consists of about ninety articulated bones 

 (united at the joints). The skull has the various bones comprising it 

 so firmly fused that they appear as a single bone. Even the seemingly 

 single bone of the fore arm will be found to consist of two bones which 

 have fused together. 



THE AXIAL SKELETON 



This is divided into the skull [cranium ( ) and 



visceral skeleton ( ) ] , and the vertebral column. The 



two divisions of the skull just mentioned are made up of the brain case 

 together with the auditory ( ) and olfactory cap- 



sules ( ). These constitute the cranium. The jaws 



and hyoid arch ( ) together, form the visceral 



skeleton. 



The inside of the cranium, where the brain is placed, is known as 

 the cranial cavity. The skull itself is composed of thirty-two bones and 

 cartilages fused together so as to appear almost a solid structure. The 

 cranial bones form the roof, walls, and floor of the cranial cavity. 



The floor is composed of the basioccipital ( ) 



and the parasphenoid ( ). 



The walls consist of the parietals ( ), the otic 



bones ( ), and the exoccipital ( ). 



The roof is made up of the supraoccipital ( ) 



and the frontals. 



The facial bones, forming the face, consist of nasals ( ), 



the premaxillas ( ), and the maxillas ( ) 



above, and vomers ( ) below. The premaxillas and 



the maxillas, however, are a part of the visceral skeleton, comprising, 

 together with a pair of quadrangulars, the upper jaws. 



H and I. Vertebrae of a frog. H, fourth vertebra, seen from in front; I, sixth 

 and seventh vertebrae from the right, as., Prezygapophysis; cen., centrum; n.a., 

 neural arch; n.c, vertebral foramen; n.s., neural spine; pz., postzygapophysis; r.c, 

 cartilage at end of transverse process; tr., transverse process. 



(A, B, C and D from Bourne, after Ecker. E, F, G, H and I, after Borradaile.) 



