35 



36 - 



35 



. / 

 X 5 \i e e 



FIG. 89. 



Kio. 90. 



FJGS. 88, 89. Reconstruction diagrams of the cranial cartilaginous skeleton in a double monster belonging to Class I., i.e. with union in the region of 

 the optic lobes. Fig. 88 is a view from above of the skeletal parts after removal of the roof cartilages by a section passing horizontally through the olfactory 

 and the auditory capsular cartilages. Fig. 88 also includes the mandibular and hyoid arches, which for diagrammatic purposes are represented as wider 

 than normal. The transverse lines numbered 35, 36, 37, 38, indicate respectively the planes and levels of the various transverse sections shown in Pis. VIII., 

 IX., figs. 35, 36, 37, 38. Fig. 89 represents the roof parts of the skull with transverse lines having the same meaning as in Fig. 88 (see explanation under 

 PI. XVII. fig. 59). The general references to Class I. will be found under PI. I. fig. 4. ( xapprox. 15.) 



FIG. 90. Diagrammatic outline of the central cavities of the brain in the same double monster as that from which Figs. 88 and 89 were taken. The 

 transverse lines have the same meaning as in these figures. The large composite cavity of the mid-brain (optic lobes) is seen to lead, in front, into the 

 cavities of the two forebrains, and, behind, into that of the single medulla (see under PI. XVIII. fig. 70). 



. 



Fie;. 92. 



FIGS. 91-93. Diagrams of the cartilaginous cranial skeleton and of the brain cavities in a double monster belonging to Class II., i.e. with union in the 

 region of the medulla. The numbered transverse lines are for the same purpose, and have the same meaning as in PI. XXI. figs. 88-90. The general 

 references to Class II. are given under PI. I. fig. 6. See also under PL XVII. fig. 61, XVIII. fig. 71. (xapprox. 15.) 



LETTERING IN ALL THE FIGURES. 



a olfactory capsular cartilage. 

 b trabeculae cranii. 

 c parachordal cartilages. 



d on trabeculae in front of the two pituitary spaces. 

 e on parachordals behind the pituitary spaces and the tendon of 

 rect. oc. ext. 



ff outer and inner palato-pterygoids. 

 ii' ,, ,, hyomandibulars. 



kk' ,, ,, periotic cartilages. 



in in the two pituitary spaces. 



gg' outer and inner Meckel's bars. 

 h h ' , , , , hyoid arches. 



). V. G. 



PL. XXI. 



