The External Anatomy of the Thylacine Facial features (continued): The rhinarium (Latin = "of the nose") is the moist, fleshy tissue surrounding the nostrils. Its function is believed to be olfactory; detecting smells and ascertaining the direction of their source.

. Rhinarium of Thylacinus from the front (A) and from above (B).

Pocock - Proceedings of the Zoological Society (1926) (Fig. 27 p. 1041). . Pocock states: "The rhinarium in Thylacinus is large, coriaceous, entirely naked, and sometimes projects prominently beyond the edge of the upper lip, towards which its anterior surface then recedes downwards and backwards. Viewed from the front ( A ), it is about as wide as high, but the inferior third of it is constricted to form a very definite philtrum about as wide as high with nearly vertical sides defined by the hair of the upper lip. The philtrum is marked by a pair of vertical parallel grooves, one on each side of the middle line, which do not ascend as high as the nostrils. The upper edge is strongly convex, from side to side, and the internarial space is wide and marked by a median vertical groove, which does not reach the summit of the upper surface above and ceases below on a level with the upper ends of the grooves of the philtrum. There is a tolerably deep infranarial area on each side. Viewed from above ( B ), its upper surface is about one fourth wider than long, its anterior edge is slightly emarginated, its posterior edge ill defined from the integument behind it, its lateral edges behind the nostrils are convex, and only a small area of the nostril is exposed. In profile view the nostrils are large and open outwards and forwards". The ears of the thylacine are erect, forward-facing, rounded and covered with short fur. The external opening is shielded by a line of longer golden-coloured hairs. Pocock provides a comprehensive description of the structure of the external ear. He opens by stating: "The ear in Thylacinus is moderately large; its height exceeds its antero-posterior width and it is attached to the head by a broad base. Its anterior edge is lightly convex up to the somewhat narrowed apex, and from the apex to its inferior point of attachment the margin is more strongly but less regularly convex". . . Ear of Thylacinus expanded, with the supratragus raised. Pocock - Proceedings of the Zoological Society (1926)

(Fig. 29 p. 1044). Anatomical features (A-D) described below. . Ear of Thylacinus (Specimen OUM 7942).

Courtesy: Oxford University Museum of Natural History.

Photo: Dr. Stephen Sleightholme. International Thylacine Specimen Database, 5th Revision 2013. . (A) anterior ridge; (B) anterior passage, which can be closed by raising ridge C against A;

(D) ridge reinforcing border of inferior passage in front of ear canal. . Pocock concludes with a detailed description of the cartilaginous structure of the external ear, and notes that the "cavity of the external ear is capable of being closed". Little is noted in the literature regarding the thylacine's eyes. George Harris (1808) states: "Eyes large and full, black, with a nictitant membrane , which gives the animal a savage and malicious appearance". William Patterson, in a letter to Sir Joseph Banks (1805), gives the measurements of the eye of his specimen: "length of the eye, which is remarkably large and black, 1 ¾ inches (4.45cm); breadth of the eye ¾ inch (1.91cm)". . . Close-up view of the thylacine's eyes - Beaumaris Zoo (QD), Hobart (1933).

Photo courtesy: David Fleay Trustees. . Hans Naarding , a field ranger with the Tasmanian Parks and Wildlife Department, sighted what he believed to be a thylacine at Togari in 1982. In his report, he made comment on the eye reflection: "Eye reflection was pale yellow". The Hamilton Spectator of the 20th June 1896 (p. 2) states with reference to the thylacine's eyes: "The eyes, which are large, are furnished with a membrane, like the eyes of owls; and this is called the nictitating membrane. This is almost continually moving in the daytime, as the eyes are exposed to more or less of sun-shine". The thylacine is unique in having the largest gape of any mammal. The gape angle is often quoted to be in the order of 120°. This however, is a gross exaggeration, as opening the jaw more than 80° would violate the integrity of the joint. . . Motion picture still of the last captive thylacine at the

Beaumaris Zoo (QD), Hobart (1933), displaying the species's "threat-yawn" response.

Image courtesy: David Fleay Trustees. . Thylacine skull (Specimen OUM 7937).

Courtesy: Oxford University Museum of Natural History.

Photo: Dr. Stephen Sleightholme. International Thylacine Specimen Database, 5th Revision 2013. The wide gape may well be advantageous in stalking fast-moving prey such as wallabies. In theory, the greater the gape, the greater the grasp, and this would vastly increase the chance of a capture and consequent kill. The gape yawn was a threat warning to indicate that an individual's presence was not wanted, and may also be related to sexual display in the male thylacine. Thylacine yawn sequence created by Arnfinn Holderer (2016), with technical contributions from C. Campbell and Dr. S. Sleightholme. Click gear button in lower right corner and select "?" to view control options for changing viewing angle and distance. This animation is copyright and unauthorized use strictly prohibited.