No. i.] MORPHOLOGY OF THE PETROSAL BONE. 17 



p. 307). It reaches that under surface, so far as can be judged 

 from the figures and descriptions, through a large opening, 

 which must be the foramen lacerum medium of the adult. 

 Jacoby's figures and descriptions (No. 16) of a much younger 

 embryo seem to confirm this. Vrolik's figures show little or no 

 indication of a division of this opening into two parts by the 

 lingula. Jacoby's figures, on the contrary, show the lower end 

 of the opening cut off as a separate foramen by a strong carti- 

 laginous bridge. The upper part of the opening in Jacoby's 

 figures is simply a wide cleft in the cartilaginous side wall of 

 the cranium, which transmits the third branch of the trigemi- 

 nus, and apparently the second branch also. The ventral, com- 

 pletely separated, part of the cleft transmits the internal carotid 

 artery, and is called by Jacoby in one place the canalis caroticus, 

 and in another the foramen lacerum anterius (No. 16, pp. 66, 

 74). That it is not the foramen lacerum anterius of Thane's 

 descriptions (No. 24, vol. ii, pt. i, p. 70) is sufficiently evident 

 to need no comment. 



In the adult man, the facial nerve does not traverse the fora- 

 men lacerum as it seems to in embryos. It is, however, still 

 exposed to that foramen at the hiatus Fallopii, and, coming 

 from the hiatus, the large superficial petrosal nerve crosses the 

 foramen to reach the posterior orifice of the Vidian canal (No. 

 24, vol. ii, pt. i, p. 70), which it traverses with a branch of 

 the external carotid artery. By the inner part of the foramen 

 the internal carotid artery enters the cranial cavity, its groove 

 being partially, and sometimes completely, separated from the 

 rest of the foramen by the lingula (No. 24, vol. ii, pt. i, p. 70). 

 The foramen spinosum and foramen ovale, both of which are 

 cut off from the foramen lacerum, and may be, even in the 

 adult, incompletely separated from it, transmit respectively the 

 large and small meningeal arteries (No. 24, vol. ii, pt. i, pp. 

 47, 80). An irregular cleft, the petro-basilar fissure, extends 

 from the foramen lacerum backward and outward to the jugular 

 foramen (No. 24, vol. ii, pt. i, p. 68). 



In Amia (No. 2, p. ooo), the facial foramen perforates the 

 petrosal and transmits both the facial nerve and the jugular 

 vein. The facial nerve does not, however, leave the cranial 



