422 THE AMERICAN MONTHLY [Dea. 



First study a sinp^le vertebra of some large fish; it 

 presents the following ])nrts: a centrwm, which is bicon- 

 cave ami jierforated in the centre. In life the space is 

 occupied with \j\\enotochord, an embryonic cartilage which 

 underlies the entire spinal system. On its dorsal side 

 the centrum carries an arch of bone, the neural arch, and 

 tliis passes above into the neural spine. The sides of 

 the arch both in front and behind carry small articulating 

 surfaces, the (^7e-and post-) zygapophyses. If the verte- 

 bra is one oi the post-abdominal series there is below the 

 centrum a corresponding haemal arch and haemal spine. 

 Now examine the spinal column of tlie smelt and after 

 locating the points just made, compare the vertebrae in 

 different parts of the spinal column and ascertain whether 

 they are all alike. In the trunk region study the ribs, 

 remove one and note its head, a rounded surface for arti- 

 culation with the centra, note also at what exact point the 

 ribs articulate with the back-bone. Do you find any in- 

 dication of a breast- bone. 



Examine the vertebrae at the line between the trunk 

 and post-abdomen, and study the transition from the 

 rib-bearing vertebrae to those having haemal arches. 

 Examine the bones at the base of the caudal fin; the row 

 of centra terminates in a long piece oi hy pur al bone Bhint- 

 ing upward with flattened neural and haemal spines 

 which are adapted to receive the fin-rays; cf. hoinocercal 

 and heterocercal types of tail. (The pectoral fin presents 

 the following bones, so small, iiowever, that the limb 

 should be studied from some fish ot large size. There 

 is a ^osi-tew;?07*aZ reaching up into the hinder part of 

 the skull, a row of bones leading down from it, the 

 clavicles to the base of the fin; a small dorsal scapula and 

 a larger ventral coracoid between the clavicles and the 

 base of the fin; three bones beyond these are called re- 

 spectively beginning with the most dorsal of the row, 

 the pro- meso- and meta-pterygium; beyond these there is 



