354 CHARLES CLIFFORD MACKLIN 



but histologically a sheet of perichondrium intervenes. There 

 is no connection with the processus alaris of the temporal region 

 through the commissura alicochlearis, such as Jacoby shows 

 in the 30 mm. stage of homo and Voit figures in his model of the 

 skull of lepus, but there is what I regard as a rudiment of this, 

 viz., the cartilago supracochlearis, (figs. 1 and 3) which will be 

 later described. The otic capsule roofs over the recessus supra- 

 alaris and recessus jugularis, and bridges the foramen jugulare 

 (fig. 5). 



In the otic capsule (figs. 6 and 7) we may distinguish a larger 

 dorsolateral portion, which contains the semicircular canals, 

 and which may therefore be known as the pars canalicularis 

 (Voit), and a smaller, ventro-median portion, which contains 

 the cochlear part of the membranous labyrinth, and which may 

 therefore be termed the pars cochlearis. Voit has restricted the 

 use of the term 'pars vestibularis' to the dorsal part of the pars 

 cochlearis, which presents the fenestrae vestibuli and perilym- 

 phatica and the fenestrae for the vestibular division of the eighth 

 cranial nerve. It contains the first, or unwound, portion of 

 the ductus cochlearis. I shall adopt this usage of the term in this 

 description. 



The cartilage of the two portions is directly continuous, the 

 zone of union being marked cranially by a notch, open above, 

 which may be known as the superior otic notch (figs. 6 and 7), 

 and ventro-laterally by a recess formed by the union of the 

 lateral surface of the pars cochlearis with the ventral surface 

 of the pars canalicularis; this may be known as the ventro-lateral 

 otic recess (fig. 6). It contains the anlagen of the auditory 

 ossicles. 



The pars canalicularis is an irregular, somewhat flattened, 

 ovoid mass of cartilage, hollowed for the passageways of the 

 semicircular canals and utriculus. It presents for examination 

 three surfaces, ventral, lateral and medial. Of these the lateral 

 and medial are convex, and are approximated above and behind, 

 their -ventral edges being widely separated. The lateral surface 

 (fig. 6) is smooth, and somewhat triangular in shape, being wider 

 above than below. The cranial border is rounded, and is formed 



