8 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



formed through a union of distinct parts, whether these be regarded 

 as pleurocentra and hypocentra or as principal and intercalated ver- 

 tebrae. 



With reference to the relations of the upper arches to the verte- 

 bral bodies, authors have not been wholly accurate. Franque figures 

 three vertebral bodies and two superior arches ; the bases of the lat- 

 ter reposing equally on the upper surfaces of two contiguous ver- 

 tebral bodies, so that the upper arches are intervertebral in posi- 

 tion. In his figure of the complete skeleton, he represents the bases 

 of all the upper arches of the dorsal region as resting in a similar 

 way intervertebrally. The bases of the succeeding simple vertebrae 

 are represented as resting almost wholly on the bodies of their 

 respective vertebrae, while the upper arches of the remainder of the 

 tail are borne by their respective intercentra. The following quota- 

 tion from Franque is produced: 



' ' Inter apophysin superiorem et corpus utrimque in parva f os- 

 sula pauxillum cartilaginis inclusum est, quod in spuriis vertebris rep- 

 eris, cui cartilaginis apophysis affixa est, et eo quidem modo ut usque 

 ad locum quendam unaquaeque apophysium duobus vertebrarum cor- 

 poribus addicenda sit." 



Shufeldt (57) reproduces Franque's figures, and states that the 

 bases of the neural arches " articulate between each consecutive pair 

 of vertebrae, these latter having a form to accommodate themselves 

 to this unique condition." Furthermore, in Franque's figures the 

 hinder border of the base of each arch is represented as coming into 

 contact with the anterior border of the next base behind. 



Schmidt refers to Franque's and Shufeldt's descriptions and fig- 

 ures. He affirms that he has not been able to find, in his specimens, 

 the upper arches either to be placed between the vertebral bodies, or 

 to come into contact by their adjacent basal borders. In both his 

 text and his figures he represents the upper arches of the whole dor- 

 sal region as sitting on the hinder half of their respective bodies, and 

 extending over the next body behind by only a little process; also, 

 as having between the successive bases, even in the region close to 

 the head, a considerable interspace. In so doing he has fallen into 

 as great an error as that of the authors whom he attempts to correct, 

 but of an opposite kind. 



When we come to examine these parts accurately, we find that 

 in the hinder portion of the tail, where pleurocentrum and hypocen- 

 trum are both developed, the neural arches have their bases ex- 

 panded anterio-posteriorly, and rest almost wholly on the hypo- 

 centra. Nevertheless, the anterior process of the base projects 



