72 ANATOMY OF VERTEBRATES. 



end of tlie notocliord 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.' ^ 



The immature Lamprey, called Sand-lance {Ammoccetes), 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, ilj. 16 : the sphenoidal arches, ib. 5, encom- 

 pass the pituitary or hypophysial space, hy, now closed 

 hj 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; 

 . , .. hut is divided from the vomerine plate, ib. 13, bv a 



Ease of slnill, -t ' ^ J 



Amnwcf.tc, backward extension of the nasal sac, ib. 19, to the 



Jliiller . . . , 



pituitary vesicle. 

 In the ]\Iyxiue the acoustic capsules are approximated at the 

 base of the skull ; the s})henoidal 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 Lancelot. 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 svipports the nasal capsule ; another 

 process extends backward to the occipital 

 cartilage. Other processes are also sent 

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

 Myxinoid cartilages.^ 



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

 cartilage is continued backward, in the form of two slender 

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

 cervical region. The hypophysial space, hi/, in front of the 

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

 verted hito 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 ai-chcs, 24, 



' Aiiscx lalcrali'K, Vogt ; FIiiiH'l-fors<'ilz<: hisis crtniii, JliUler. 

 * I'liiijiicfficialc, Yogt; Gaiimciipliilli; filulkr. ■' xxi. 



of ^kul], ADunocdc, 



MllllLT 



