Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 273 



of the nervus acusticus. The anterior semicircular canal and the 

 anterior part of the posterior one are, as already stated, pressed 

 against and slightly imbedded in the lateral surface of the brain. 

 The anterior semicircular canal and the sinus utric. superior li« 

 entirely in the cranial cavity, as does also all of the utriculus 

 excepting its hind end. The sacculus lies in the saccular groove 

 in the floor of the cranial cavity. The external semicircular canal 

 is almost entirely enclosed in a bony or cartilaginous canal, as is 

 also the larger part of the posterior one. Whether there was a 

 membrane separating the labyrinth from the cranial cavity proper, 

 or not, could not be determined. 



No ductus endolymphaticus could be found in any of the 

 several dissections made. 



The nervus acusticus arises from the lateral surface of the 

 medulla ventral to and between the lateral-sensory root of the 

 trigemino-facial complex and the root of the nervus lineae lateralis 

 vagi. It runs at first almost directly downward, and, because 

 of the position of the ear, close against the lateral surface 

 of the brain ; the anterior part of the nerve then turns 

 laterally while its posterior part turns mesially, giving to the 

 nerve a twisted appearance. The anterior part of the nerve has 

 two long branches, which innervate the cristse acusticse in the am- 

 pullae of the anterior and external semicircular canals, and a short 

 portion between them, which innervates the macula acustica of the 

 recessus utriculi. The posterior portion of the nerve sends stout 

 branches to the macula acustica sacculi, and to the macula or 

 papilla acustica lagense, and a more slender one to the crista 

 acustica in the ampulla of the posterior semicircular canal. What 

 I take to be a macula neglecta could be recognized in one of several 

 specimens examined. It was innervated, in that specimen, by a 

 short branch of the branch that innervated the crista acustica of 

 the posterior semicircular canal. 



There is a large otolith in the sacculus, and, in the lagena, a 

 compact mass of material which, when touched, breaks up into 

 a sand-like substance. • 



