1897] MICROSCOPICAL JOURNAL. 3I 



13, The Axial Skeleton.' — After setting aside the 

 limbs, clean the back-bone in a specimen which has been 

 boiled to soften the muscular tissue, removing all the 

 flesh by picking it away or with a brush. Take care not 

 to dislocate the bones and especially not to loosen the 

 very rudimentary ribs in the trunk region. 



Note the series of vertebrae running from the head to 

 4he tip of the tail. They are less similar in different 

 parts of the column than in the fish; being differentiated 

 into regions to some extent though less markedly than in 

 the birds and mammals. In the neck cervical region, an 

 Mtlas articulating with the skull and an axis next behind 

 ihe atlas are present. Behind these come the vertebrsB 

 •f the trunky which correspond with the dorsal s^ndi lumbar 

 series of mammals; a single sacral vertebra follows and 

 toit the pelvic girdle is attached; this in turn is fol- 

 lowed by tie caudal series. Count the number in each 

 of the regions and compare with other individuals to de- 

 termine the degree of constancy of the number. 



Any of the trunk vertebree can be examined as a rep- 

 resentative case. It presents a centrum; a neural arch, 

 bearing a spine and the zygapophyses\ a bi-furcated trans- 

 verse process is carried by the centrum on each side; to 

 which the rib when present is articulated. Tranverse pro- 

 cesses are wanting in the atlas and axis\ and the neural 

 spine is unlike that of the rest of the series; the axis 

 bears a prominence in front of its centrum, the odontoid 

 process. The sacrum is like the others but has much en- 

 larged tranverse processes. The caudal series is much 

 compressed; i\\Q,'[Q'\^ ^ %qx\q^ ^i cJievronbones^ the haemal 

 spines; and the accessory parts gradually fade out and dis- 

 appear posteriorly till nothing but tiie centrum is left. 

 Ribs SLve present articulating with vertebrae in the neck 

 as well as in the dorsal and lumber regions, so that the 

 differentiation as in the mammals is not found here; the 

 ribs are rudimentary and do not run out onto the body 



