72 ANATOMY OF VERTEBRATES. 



end of the notochord the basal cartilages, developed in continua- 

 tions of its capsule, diverge, surround the pituitary vesicle, and 

 meet in front of it, forming the ' sphenoidal arches,' ' which join, 

 or expand into the ' vomerine plate.' 2 



The immature Lamprey, called Sand-lance (Ammocoetes), retains 

 a like condition of the skull, fig. 58, to the second or third year. 

 The occipital cartilages extend from the sides of the pointed end 

 of the notochord, ib. ch, and expand into the acoustic 

 capsules, ib. 16 : the sphenoidal arches, ib. 5, encom- 

 pass the pituitary or hypophysial space, hy, now closed 

 by a membrano-cartilaginous plate, and unite anteriorly 

 to form a small vomerine plate, ib. 13, in front of 

 which is the single undivided nasal capsule, ib. 19* 

 The now expanded cerebral end of the neural canal, 

 fig. 59, n, is still defended by fibrous membrane only ; 

 but is divided from the vomerine plate, ib. 13, by a 



Base of skull, , r ., i 



Ammocete, backward extension of the nasal sac, ib. 19, to the 



-Muller . . 



pituitary vesicle. 

 In the Myxine the acoustic capsules are approximated at the 

 base of the skull ; the sphenoidal arches are longer, and unite with 

 the palatine plate and arches, from which are sent off the labial 

 cartilaginous processes supporting the buccal tentacles homologous 

 with those in the Lancelet. In the long hypophysial interspace of 



the sphenoidal arches a more or less firm 

 cartilaginous plate is developed, from which 

 a slender median process is continued for- 

 ward to the vomerine or palatine plate, 

 which supports the nasal capsule ; another 

 side view of skuii, Ammocete, process extends backward to the occipital 



Mffller r i 



cartilage. Other processes are also sent 

 off from the sides, which form a complex system of peculiarly 

 Myxinoid cartilages. 3 



In the mature Lamprey {Petromyzoii), fig. 60, the occipital 

 cartilage is continued backward, in the form of two slender 

 processes, c, upon the under part of the notochord, ch, into the 

 cervical region. The hypophysial space, hy, in front of the 

 occipital cartilage, remains permanently open, but has been con- 

 verted into the posterior aperture of the naso-palatine canal. The 

 sphenoidal arches, 5, are very short, approximated towards the 

 middle line ; and the vomerine cartilage, 13, is brought back 

 closer to the sphenoidal arches. Two cartilaginous arches, 24, 



1 A?ises laterales, Vogt ; Fliigel-forslltze basis cranii, Muller. 



2 Plaque faciale, Vogt; Gaumenplatte, Muller. 3 xxi. 



