OSTEOLOGY OF THE ARMOEED DINOSAUKIA. 91 



Dermal Aemok. 

 Plates 2, 3, 4, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, and 25. 



The exoskeleton of Stegosaurus consists primarily of four types of structure; 

 the so-called gular or throat scutes covering the neck and possibly the head (pi. 22, 

 figs. 2 and 3) ; the isolated rugose ossicles which have not been placed but probably 

 were scattered over the skin (fig. 56); the series of erect plates forming two rows 

 along the neck, back, and tail (pi. 14) ; and the elongated, spike-like spines placed 

 near the end of the caudal series (pis. 15 and 16) . 



Dermal ossicles (o.). — The first type, consisting of small, depressed, angularly 

 rounded ossicles, was found in the rock near the skull and neck of No. 4934 (pi. 2, 

 ako pis. 3 and 4, o). These ossicles are of irregular sizes, but none exceeds 35 mm. in 

 diameter (see fig. 55). It might be mentioned that similar ossicles were found with 

 the skeletons of three other individuals, Nos. 4936, 7615, and 7947, in the collec- 

 tion of the National Museum. (See two of these in pi. 22, figs. 2 and 3.) 



Nearly all of these structures have one flattened side with a sculptured surface, 

 but without distinct pattern. The pits and grooves forming the sculpture are most 

 pronounced in the center of each ^ 



ossicle. From the position of ^^^ 



some few of these that still re- ^^m 



main attached to the cervical ver- ^S^^ 



tebrae by matrix, i am led to be- ^^^ 53._deemal ossicle of stegosaueus trNGuuATus maesh. ^ nat. 



lieve that the flat, sculptured face size, a, Supeeioe view; b, side view; c, infeeioe view. If the 

 , , 1 , 1 • J 1, scale is coeeectly given this is an exceptionally laege ossicle. 



represents the external side shown j^^^ maesh. 

 in plate 22, figure 2. If this be 



correct the patches of ossicles present on either side of the neck, as shown in plates 

 2 and 3, o, have their internal surfaces uppermost (pi. 22, fig. 3). There is no posi- 

 tive evidence to show that they were confined to the under side of the jaws and 

 throat as indicated by Marsh in his restoration of Stegosaurus (pi. 32, upper figure). 

 From the position of those found with No. 4934, it would appear more probable that 

 they covered the sides of the neck from the base of the erect plates downward, 

 scattering, if at all, on the ventral areas, this region being protected by softer skin 

 without bony scutes as in most modern reptiles. 



After a careful comparison of the Heloderma skull and its investing skin tubercles 

 (compare figs. 1, 2, and 3, pi. 22) with those of Stegosaurus, it appears probable that 

 these ossicles formed a similar investiture of the superior portion of the Stegosau- 

 rian cranium. Tjiere may have been evidence bearing on the above suggestion, but 

 when the skull came into my hands it had been entirely divested of its matrix, thus 

 destroying all traces of closely associated ossicles. 



That these extended to other parts of the body is shown by ossicles found near 

 the tenth and eleventh vertebrae and stiU others attached to the sixteenth verte- 

 bra, and more posteriorly two were found at the base of the tenth plate near its 

 posterior border. That they did not form a continuous investiture of the sides of 

 the animal is shown by their absence from the matrix between the ribs of the left 

 side and the underlying dorsal armor, for surely the skin must have been present 

 here when the carcass was entombed. 



