LIMIOOLiE ■ 351 



basipterygoid processes or occipital fontanelles,^ but with 

 well-marked grooves for supra-orbital glands. . In Lestris 

 antarcticus at any rate there is a foramen formed round 

 anterior end of supra-orbital groove, as in Chionis (q-v.) In 

 Lestris there is a distinct tendency towards the pseudo-holo- 

 rhinal condition of the Thinocoridse and Glareolidse. 



In Larus the relations of the clavicles, scapula, and cora- 

 coids are as in the Charadriidse ; but the clavicles provided with 

 a hypocleidium come into nearer relations with the carina 

 sterni, to which they are attached by a ligament. The cora- 

 coids are in contact behind the spina (externa) sterni. The 

 same statement may be made of Lestris. 



The cervical vertebra are fifteen in number. The dorsal 

 vertebrae are, as in Alcidse and plovers, opisthocoelous. Six 

 {Lestris antarcticus) or seven ribs articulate with the sternum. 

 The first phalanx of the second is commonly perforated.^ 



As to the pterylosis, the plan is that of the Limicolse, but 

 the ventral tract does not divide until some way down the 

 neck. The feet are webbed, the hallux is small or absent, 

 and there are twelve rectrices. 



The muscular formula oi Bissa tridactyla is AX-f- ; of 

 Larus, Stercorarius, a,ndGygis, AXY-I-. The other genera 

 have the complete formula ABXY -|- . Bhynchops has no 

 ambiens. 



In Lestris crepidatus and L. antarcticus the semi- 

 membranosus is sometimes two-headed, one arising from 

 ischium and one from postacetabular ridge of ilium. 



The tensores patagii ^ (see fig. 171) are on the plan of 



' These are present in the young : see Parkeb, Linn. Trans. (2)„ i. p. 142. 



^ This does not, however, as it has been stated to do, distinguish the LaridiE 

 from other Limicolse ; though apparently universal in the gulls (including 

 Anous and Gygis), the same perforations are found in Glareola. The value of 

 this anatomical fact maybe judged by the perforation of the same bone in such 

 varied types as Pterocles, Coracopsis ohscura, {not in C. nigra), Psittacula 

 pasxerina, Machcerhamphus Andersoni, Heliodilus, Caprimulgus, Phaethon 

 candidus {not P. ruhricauda) , and Fregata minor. These instances are taken 

 from the osteological plates illustrating MM. Gkandidier and Milne-Edwaeds's 

 Histoire NatwelU de Madagascar. 



^ For muscular anatomy of LaridiB see Giebel, ' Beitriige zur Anatomie 

 d. Moven,' &o., Zeitschri /. d. ges. Naturw. a. (1857), p. 20 ; Beddaed, ' A 

 Contribution to the Knowledge of the Anatomy of Bhynchops,' P. Z. S. 189C, 

 p. 299. 



