no PATTEN AND REDENBAUGH. [Vol. XVI. 



proximally, with the posterior border of the endocranium and 

 are attached distally to the posterior sides of the chilaria. 



Near the posterior extremity of the endocranium are two pairs 

 of foramina (Text-figs. 3-5 ; Pis. VI and VIII, Figs, i, 3, and 4, 

 f.^) which afford a passage for intestinal nerves {i.n.^7). 



b. The Abdominal Endochondrites. 



These are six in number (Text-figs. 5 and 6; Pis. VI, VIII, 

 and IX, Figs, i, 3, 4, and 6, a.e.^''^), metamerically arranged 

 in the median line neural to the ventral cord, one at the base 

 of each pair of abdominal appendages {ap.^-'^). It will be 

 noticed that they lie upon the side of the central nervous sys- 

 tem opposite to that on which the endocranium lies. They are 

 fibroid in structure, like the endocranium, and act as centra for 

 the attachment of the internal branchial muscles (Text-figs. 5 

 and 6 ; PI. IX, Fig. 6, i.b.ni. ^''^), longitudinal abdominal muscles 

 (Text-figs. 5 and 6; Pis. VI, VIII, and IX, Figs, i, 4, and 6, 

 l.a.m.), and haemo-neural muscles (Pis. VI, VIII, and IX, Figs. 

 I, 4-6, h.n.m.^''^). 



c. The Branchial Cartilages . 



These structures were described by Gegenbaur in 1858. 

 Lankester {Qnar. Jonrn. Micr. Sci., 1884) described a "pair 

 of ligamentous bands, the entapopJiysial ligaments, which pass 

 from one to another of the dorsal ingrowths of the integu- 

 ment known as the dorsal entapophyses." "The ligamentous 

 band is not of equal dimensions throughout, but where it is 

 attached to an entapophysis it gives off at right angles a 

 conical, knob-like protuberance." 



This ligament is continuous only between the first and sec- 

 ond pairs of entapophyses. From the outer side of every enta- 

 pophysis except the seventh, a cartilaginous bar (Text-figs. 5 

 and 6 ; Pis. VI and IX, Figs, i and 6, b.c.^~'^) passes neurally 

 to the inside of the appendage of the same metamere ap.^~'^. 

 It acts as a skeletal support for the appendage and also for 

 the attachment of numerous muscles. These bars consist of a 

 highly characteristic core of capsuliginous cartilage enveloped 



