THE ANATOMY OF A HABIMERHEAD SHARK. 977 



duct but leads into the posterior perilymph cavity. This obser- 

 vation agrees with that of Goodey (6) on the postei'ior duct in 

 Ghlmnydoselachus anguineus. 



The Utricidus, as in nearly all Elasmobranchs, is divided into 

 two portions, anterior and posterior, which do not communicate 

 directly Avith one another, but indirectly through the sacculus. 



The anterior utricle (u.a.) is circular in transverse section and 

 gives off the anterio?' canal (c.a.) at its dorsal end. The canal 

 runs forward and slightly outward, and expands at its lower end 

 into the antei'ior ampulla (a.a.). The anterior utricle and the 

 anterior canal together form an oval. 



The anterior utricle also gives off posteriorly, at about the 

 middle of its length, the external canal (c.e.), which runs at first 

 downward and outward, and secondly horizontally. At its 

 anterior end it expands into the external ampulla (a.e.), which 

 communicates again with the anterior utricle through a short 

 canal running dorsal to the recessus utriculi, but having no direct 

 connection with it. 



On the ventral side of the anterior utricle is a fac, the recessus 

 uti'iculi (r.u.), which is somewhat flattened from side to side, and 

 almost triangular in lateral view. It communicates with the 

 anterior utricle through a small aperture, whilst another small 

 aperture, situated near the opening into the utricle, opens into the 

 sacculus. 



The posterior utricle {u.p.) is the portion of the labyrinth 

 situated nearest to the median longitudinal line of the cranium. 

 It has direct communication Vv'ith the sacculus through a short 

 duct, the ductus idriculo saccularis posterior (d.u.s.p.). The dorsal 

 end of the posterior utricle gives off' the j^osterior canal (c.p.), 

 which runs downward and outward and after expanding into the 

 posterior ampulla (a.p.) opens into the ventral end of the utricle. 



The sacculus (s.) and lagena (l.) are laterally compressed ; the 

 latter being given off as a simple pouch at the infero-posterior 

 end of the sacculus. The outer face of the sacculus and lagena is 

 directed outward at an angle to the median plane. 



Nerve Supply. 



The membranous labyrinth is supplied by branches of the 

 eighth cranial nerve. 



The main nerve gives off a branch which runs beneath the 

 recessus utriculi and then bends upward. It then bifurcates to 

 form the ramulus avijndla anterior (r.a.a.) and the ramulus 

 ampidla externus (r.a.e.). A longer and finer branch, the ramidtis 

 ampidla posterior (^r.a.p.'), comes off from the main nerve and runs 

 on the inner side of the sacculus to the posterior ampulla., giving 

 off tiny ramuli to the sacculus and lagena en route. We were 

 unable to trace the ramidus ittrictdi in our specimen, and it is 

 probably very small. 



The membranous labyrinth resembles in many respects that of 

 Cestracion philippi. 



