3i6 



ENDOCRANIUM, BRANCHIAL AND NEURAL CARTILAGES. 



deeply grooved on the haemal side. Along the whole haemal side of the process 

 are attached two large muscles that go to the first pair of entapophyses. To the 

 body of the endocranium, on both sides of the basioccipital, are attached longi- 

 tudinal abdominal muscles. Their attachments extend a litde anterior to the 

 hffimal processes. In front of this, the body of the endocranium is destitute of 

 muscles on the haemal side. A pair of small chilarial muscles are attached to 

 the haemal side of the extremity of the basioccipital. 



Fig. 21$. — Endocranium of Limulus. A, Seen from the neural surface; B, from the heemal surface; C, from the 



caudal end. 



The occipital ring, oc.r., begins at the points where the marginal walls meet 

 the posterior-lateral processes. Here two vertical outgrowths are formed which 

 unite with each other on the neural side of the ventral cord. At their bases the 

 processes are slender, but distally they enlarge and thicken, forming a polygonal, 

 supraoccipital plate that is joined to the capsuliginous bars, B, by strands of 

 connective tissue. Upon the neural surface of the supraoccipital plate are two 

 depressions, to which are attached a pair of muscles going to the insides of the 

 chilaria, ch.m. From the anterior edge of the plate, muscle strands pass for- 

 ward to the integument immediately behind the mouth. 



The capsuliginous bars, B, arise from the thin posterior margin of the endo- 

 cranium, bend neurally and slightly toward the median line, and are attached to 



