INTERNAL ANATOMY. 



37 



tion and supination of the buccal cirri, consist of two por- 

 tions, an inner and an outer (Fig. 17). The outer one, 

 by whose contraction the cirri are retracted in such a way 

 that they come to lie across the entrance to the mouth, 

 those of one side interlacing 

 with those of the other so 

 as to form a perfect barrier 

 to the mouth, is a powerful 

 muscle lying outside the 

 bases of the cirri. The 

 inner muscle, which appar- 

 ently serves to erect the 

 cirri, consists of distinct 

 muscular tracts lying be- 



whose fibres interlace with those of the 



tween every tWO Consecutive velar sphincter (z/.#). /./. Inner muscle 

 c j n -i (m. internus). 



The sphincter muscle of the velum has been already 

 referred to. (Cf. Fig. 7.) A sphincter muscle of a simi- 

 lar character also surrounds 

 the anus. 



The septa which separate 

 the myotomes from one 

 another are composed of 

 fibrous connective tissue. 

 The fibres are imbedded in 



Fig. 17. Muscles of the oral hood. 

 (After LANGERHANS.) 



m.e. Outer muscle (m. externus) 



,0 



Fig. 18. -Diagram illustrating the ge l a tinOUS matrix, 

 different layers of the integument. (After 



HATSCHEK.) salient feature in connexion 



/. Epidermis. 2. Outer layer of cutis 

 (basement membrane of Hatschek and wlt " the entire Connective 



Sp H-T IK 3 ' Midd i le lay T" f cu l is whh tissue-system of Amphioxus 



radial fibres. 4. Inner layer of cutis. J 



5. Epithelial layer of cutis (limiting mem- is the great preponderance 



brane). 



of the gelatinous element. 



It forms the bulk of the dorsal and ventral fin-rays, and 

 of the cephalic and caudal integumentary expansions. 



The 



