notochord 



nasal capsule 

 posterior tectol cartilage 

 posterior lateral cartilage^ 

 anterior tectol cartilage 

 annular cartilage 



first bronchial arch 



anterior lateral cartilage 



velar skeleton 



notochord 



first bronchiol 

 arch 



extrohyoid arch 



A* hyomandibulor branch VII 



cornuol cartilage 



velar skeleton 



orbital cartilage 



nasal capsule 



posterror />f^ \ 1 ' 



lateral cartilage XT' \ ^ ^.^3 - L ^ 1 



posterior tectol cartilage 

 notochord 



anterior tectol cartilage 



first bronchial arch 



annulus trematicus 

 otic capsule 



anterior lateral cartilage' 



styloid cartilage 



apical cartilage 



posterior lateral cartiloge 

 spinous cartilage 



NNv^velor cartilage 



copular cartilage 



■piston cartilage 



Figure 5-27. Stages in the development of the head skeleton of the lamprey. A, B, lateral and 

 ventral views of 8 to lO-mm larva; C, lateral view of early metamorphic larva; D, lateral view of 

 late metamorphic larva; E and F, lateral views of adult head and tongue elements. (After Johnels, 

 1948) 



connective tissue to the ventral surface of this commissure. 

 From the anterolateral angles of the commissure a cornual 

 process extends out and forward. 



Attached to the inner aspect of the subocular visceral 

 plate by ligaments is a complex of several cartilaginous rods 

 which extend back and medially into the velum. The velum 

 lies between the opening of the nasohypophyseal duct into 

 the mouth and the pharynx; it extends backward into the 

 pharynx. Its margins roll and unroll so as to pump water 

 from the mouth cavity into the pharynx. 



The nasal sac and nasal duct are enclosed in a fenes- 

 trated capsule and a series of loops. Below these is a laterally 

 compressed rod forking anteriorly into two tentacular rods; 

 this is the subnasal cartilage. The posterior end of the sub- 

 nasal cartilage lies just anterior to the tip of the hypophyseal 

 cartilage. The latter underlies the hypophyseal duct and, 



about midway along its length, attaches to the trabecula of 

 either side. 



Below the endocranium is an extensive tongue skeleton. 

 This is joined to the neurocranium through the external 

 division of the first branchial arch. This arch attaches to the 

 posterolateral angle of the median lingual cartilage. Ante- 

 rior to this plate are two pairs of anterior lingual cartilages 

 — lateral and medial. The medial pair is fused anteriorly. 

 The anterior margins of the lateral plates give rise to rods 

 which extend anteriorly. These divide distally into dorsal 

 (nasal) and ventral (oral) tentacular rods. Posterior to the 

 median basal plate is a midline, trough-shaped posterior 

 lingual cartilage of soft white cartilage. Far back in the 

 tongue musculature is a small ventral midline splint of 

 cartilage. 



Above the anterior plates is the dental plate. This is 



132 • THE HEAD SKELETON OF FISHES 



