THE ENDOCRANIUM OF APUS. 313 



is a thick plate of fibre-cartilage, without an occipital ring, located just behind 

 the mouth, between the central nervous system and the intestine. The body of 

 the endocranium is elongated in a transverse direction, its flaring ends giving 

 attachment to the powerful adductor muscles of the mandibles. 



A pair of chitenous apodemes, apo., project into the posterior side of the 

 endocranium. They are ectodermic invaginations lined with chitin, formed be- 

 tween the bases of the first and the second pair of appendages. From the inner 

 ends of the apodemes, a pair of tendenous cords run directly through the body 

 of the endocranium, at right angles to its fibers, emerging on the anterior side as 

 the anterior cornua, ac. 



The endocranium terminates posteriorly in a thin membrane w t which is 

 attached to the integument between the nerve cords. 



Longitudinal muscles of the abdomen are attached to the posterior sides of 

 the apodemes and to the endocranium itself. A process on the neural side of 



I 



I 1 



,- 



B 



FIG. 212. Endocranium of Apus; A, Neural surface; B, haemal surface. The mandibular muscles are at- 

 tached to the large transverse processes, m; maxillary muscles to the small processes, x. A pair of chitenous en- 

 topophyses, apa., are imbedded in the posterior side of the endocranium. X 27 1/2. After Patten and Redenbaugh 



each apodeme serves for the attachment of muscle strands going to the inside 

 of the second pair of maxillae, x. Haemo-neural muscles are attached to the haemal 

 sides of the apodemes, and a pair of muscles, inserted on the posterior neural 

 portion of the endocranium, y., pass between the nerve cords to the integument 

 just back of the first cross commissures. 



Endocranium of Mygale (Fig. 213.) The endocranium of Mygale is a 

 large oval plate of fibro-cartilage with crenate margins; like that of Apus, it lies 

 between the alimentary canal and the central nervous system. 



The neural surface is concave and provided with paired, plate-shaped 

 processes, A, n.pl. From about the middle of the large anterior cornua, arise a 

 pair of neural processes, n.pr' ', which bend around the brain and attach them- 

 selves to the integument close together on the neural side. They probably 

 represent the lateral portion of the occipital ring of Limulus. 



On the haemal side, J5, two high, flaring ridges converge toward the posterior 

 end of the endocranium, forming a deep gully in which lies the alimentary tract. 



