316 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



Arising from the middle of the cephalic border is the pro- 

 cessus entoglossus or anterior extension. This is a fine, taper- 

 ing, cartilaginous rod. It measures about 8 to 10 m.m. in 

 length and ends in a fine point. (Fig. 1 A.) 



From each extremity of the body and extending caudally, 

 arises the paired processus retrobasalis or the posterior horns 

 (Huxley). These are fairly firm, cartilaginous rods which 

 gradually taper to a fine point at their caudal extremity. They 

 are 18 to 22 m.m. in length. Near the cephalic extremity they 

 lie in close approximation showing a groove dorsally between 

 them but only a fine slit ventrally. They are bound together 

 by firm connective tissue. More caudally the distinction be- 

 tween the dorsal and ventral aspect is lost. They closely ap- 

 proximate each other, yet are easily separated with a teasing 

 needle. These cartilages are rather stiff in their cephalic 

 third but become more and more flexible distally. (Fig. 1 

 A, B, C.) 



The anterior horns or cerato-hyals arise from the extremi- 

 ties of the body or basi-hyal with which they are continuous. 

 They are divided into two parts which are separated by a 

 movable joint. (Fig. 1 A, B, C.) The first part, which is 

 continuous with the body, is a short, tapering, cartilaginous 

 rod measuring 1.5 to 2 m.m. and terminating bluntly. It runs 

 cephalad, laterad and slightly dorsad. The angle formed by 

 it and the corresponding horn is about 60 degrees. The 

 second part, also cartilaginous, is attached to the first by a 

 joint capsule allowing fairly free movement. This part ex- 

 tends laterad and caudad, tapering as it approaches its ex- 

 tremity, thence curving dorsad. With the first part it forms 

 an angle of about 75 degrees. (Fig. 1 A, B. C.) 



The posterior horn, middle horn (Huxley) or cerato- 

 branchial articulates with the basi-hyal at the junction of the 

 anterior horn and the processus retrobasalis. This structure 

 is a fine, tapering, osseous rod, measuring 12 m.m., with a 

 rounded, cartilaginous epiphysis at the proximal extremity 

 and a pointed epiphysis at the distal extremity. There is a 

 medullary cavity in the compact bone. The joint formed 

 with the basi-hyal is surrounded by a fibrous capsule allowing 

 a great range of motion. This horn runs nearly parallel with 

 the posterior part of the anterior horn. (Fig. 1 A, B, C.) 



