INTERNAL ANATOMY. 



37 



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

 tions, an inner and an outer (Fig. 17). Tlie 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 ,^f «; f •-^'"'^r' '*'' °''' ''°°''' 



' (After Langerhans.) 



muscular tracts lying be- >"■<:■ Outer muscle (m. externus) 



whose fibres interlace with those of the 

 tween every two consecutive yelar sphincter (y.sp). m.i. Inner muscle 



cirri, ("'• i"'^™^)- 



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 



ditWn,H'~°fT"", "'"'"'""f.f"' a gelatinous matrix. The 



nitterent layers of the integument. (After ^ 



hatschek.) salient feature in connexion 



/. Epidermis. 2. Outer layer of cutis . 



(basement membrane of Hatschek and With the entire connective 



Spengel) j. Middle layer of cutis with tisSUC-SyStem of AmphioxUS 



radial hbres. ./. Inner layer of cutis. -' ' 



J. Epitheiiaiiayer 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. 



