x RESPIRATORY ORGANS 
to 
ioe) 
= 
epithelium which is partially 
ciliated. The inter-branchial 
septa are much thicker than in 
Elasmobranchs, and include not 
only the walls of adjacent sacs 
and the branchial muscles, but 
also contain cavernous — peri- 
branchial lymph-sinuses. The 
cartilaginous branchial skeleton 
is situated wholly external to 
the gill-sacs, the so-called 
branchial arches lying between 
the external apertures of the 
sacs, and directly beneath the 
superficial skin, or, in other 
words, on the outer margins of 
the inter-branchial septa, and 
not on the inner, as is invari- 
ably the case with the branchial 
arches: of Fishes. 
In the Hag-Fish (Myzine) 
(Fig. 163), there are usually 
six, very rarely seven, pairs 
of gill-sacs, all of which open 
directly into the pharynx, and 
not into a branchial canal as in 
the Lampreys. On the other 
hand, Myzine is unique in 
having the outer extremities 
of its gill-sacs produced into 
a cerresponding number of 
tubular canals which, after a 
longer or shorter course ob- 
liquely backwards and out- 
wards, unite to form on each 
side a ventrally - situated ex- 
ternal aperture (Fig. 163). 
In the same genus a_ short 
canal, or oesophageo-cutaneous 
duct, passes from the pharynx 
pe aii: a RUAN hay enero att 
ty thy if, GLA 
v4 a ~\ 
Yh Y 
y, ~ : J, NS . 
sbh.0C.a 
cbrt brap orb 
oes.cl.d. 
Onsd 
lgur 
WUC 
p.l.c, posterior lateral 
K. Parker, from Parker and Haswell’s Zoology. ) 
br.ap, left branchial aperture ; 67.6, rudiment of branchial 
n.t, neural tube ; oes.ct.d, oesophageo-cutaneous duct ; 
(After W. 
au.e, Auditory capsule ; 
basket ; b7.s. 7, first gill-sac ; ¢.br.¢, common branchial tube ; ev.c, cornual cartilage ; gu/, gullet; hé, heart ; 2y.m, lingual muscles ; m.v.0, 
Dissection of Myaine glutinosa from the left side. 
cartilage ; sb.oc.a, subocular arch ; sp.c, spinal cord ; st.p, styloid process. 
median ventral cartilage ; na.¢, nasal tube; 2ch, notochord ; 
163 
Fig. 
