Prof. 0. C Marsh — A New American Jurassic Dinosaur. 103 



The quadrate is elongated, slender, with its lower end projecting 

 very remarkably forward. In front, it has a thin place extending 

 inward, and overlapping the posterior end of the pterygoid. 



The quadrato-jugal is an elongate bone, firmly attached posteriorly 

 to the quadrate by its expanded portion. In fion of the quadrate, it 

 forms for a short distance a slender bar, which is the lower temporal 

 arcade. 



The palate is very high and roof-like, and composed chiefly of the 

 pterygoids. The basi-pterygoid processes are elongate, much more so 

 than in the other genera of Sauropoda. 



The pterygoids have a shallow cavity for the reception of these 

 processes, but no distinct impression for a columella. Immediately 

 in front of this cavity, the pterygoids begin to expand, and soon form 

 a broad, flat plate, which stands nearly vertical. Its upper border is 

 thin, nearly straight, and extends far forward. The anterior end is 

 acute, and unites along its inferior border Avith the vomer A little 

 in front of the middle, a process extends downward and outward for 

 union with the transverse bone. In front of this process, uniting 

 with it and with the transverse bone, is the palatine. 



The palatine is a small semi-oval bone fitting into the concave 

 anterior border of the pterygoid, and sending forward a slender process 

 for union with the small palatine process of the maxillary. 



The vomer is a slender, triangular bone, united in front by its base 

 to a stout process of the maxillary, which underlaps the ascending 

 process of the premaxillary. Along its upper and inner border, it 

 unites with the pterygoid, except at the end, where for a short dis- 

 tance it joins a slender process from the palatine. Its lower border is 

 wholly free. 



The Brain. — The brain of Biplodocus was very small, as in all 

 Dinosaurs from the Jurassic. It differed from the brain of the other 

 members of the Sauropoda, and in fact from all other known reptiles, 

 in its position, which was not parallel with the longer axis of the 

 skull, as is usually the case, but inclined to it, the front being much 

 elevated, as in the Ruminant mammals. Another peculiar feature of 

 the brain of Diplodocus was its very large pituitary body, enclosed in 

 a capacious fossa below the main brain case. This character separates 

 Diplodocus at once from the Atlantosauridce, which have a wide pitui- 

 tary canal connecting the brain cavity with the throat. In the 

 MorosauridcR, the pituitary fossa is quite small. 



The posterior portion of the brain of Diplodocus was diminutive. 

 The hemispheres were short and wide (Figure 2), and more elevated 

 than the optic region. The olfactory lobes were well developed, and 

 separated in front by a vertical osseous septum. The very close 

 proximity of the external nasal opening is a new feature in Dinosaurs, 

 and appears to be peculiar to the Sauropoda. 



The Loiver Jaws. — The lower jaws of Diplodocus are more slender 

 than in any of the other Sauropoda. The dentary especially lacks the 

 massive character seen in Morosaurus, and is much less robust than 

 the corresponding bone in Brontosaurus. The short dentigerous 

 portion in front is decurved (Figure 1), and its greatest depth is at 



