BIRDS OF NORTH AND MIDDLE AMERICA 225 



ischia; biceps slip specialized (as in Alcidae), ending freely on pata- 

 gial membrane ; relations of biceps cruris peculiar ^ ; thigh-muscle for- 

 mula ABX+ (the ambiens, femorocaudal, accesory femorocaudal, and 

 semitendinosus muscles present, the accessory semitendinosus muscle 

 absent) ; deep plantar tendons of types II or X, remarkable in that 

 both tendons split into three branches for the three digits before they 

 unite, the slip to the hallux being previously given off from the flexor 

 hallucis ; tensor patagialis brevis a single individual tendon possessing 

 not more than an indication of a patagial fan (in Heliomis only) ; 

 extensor secundariorum present, the aneonaeus anchored to the 

 humerus; caeca present, long; liver with right lobe larger than the 

 left; gall bladder present (in Heliomis — absent in Podica?) ; syrinx 

 typically tracheobronchial. 



Pterylosis essentially ralline; neck almost continuously feathered, 

 with only a short ventral apterion; dorsal pteryla strong between 

 scapulae, forked, the posterior portion of the tracts scarcely joining 

 the anterior ones, and fused or coalesced for some distance in front 

 of oil gland, the latter tufted; aftershaft absent; whig eutaxic 

 (quintocubital) ; rectrices 18 or more; plumage in general close-set 

 and ducklike. 



Nidification of Heliomis unknown, but young said to be gym- 

 nopaedic.^ 



"The sun-grebes are a small group of tropical water birds whose 

 relationships are uncertain. Most authorities place them near the 

 Eallidae ; but Dr. Stejneger and the late Professor Forbes, for want 

 of a better place, align them close to the Colymbidae, which they 

 resemble in some of their habits and in their lobed or scalloped toes. 

 They hare little resemblance, however, to either of these groups, their 

 general make-up, especially the slender, closely feathered neck and 

 fan-shaped, rigid tail being more suggestive of the Anhingidae, 

 which the Heliornithidae further resemble in some of their habits, 

 especially that of perching upon dead trees or snags overhanging 

 streams or partially submerged therein. Tliis resemblance, however, 

 does not indicate near relationship." (E. R.) 



Family HELIORNITHIDAE : Finfoots or Sun-grebes 

 =HeUornthidae Bonapabte, Consp. Gen. Av., ii, 1857 [1855], 181.— Fdebbinqeb, 

 Unters. Morph. Syst. Vog., ISSS, 1236.— Gauow, in Bronn's Thier Keiclis, Vog. 

 ii, 1S91, 191, 300 ; Classlf. Vertebr., 1898, 35.— Wetmore, Proc. U. S. Nat. Mus., 



'Biceps very large, with three separate insertions on the leg: (1) The ordinary 

 insertion through a perfectly normal sling; (2) just anterior to this tendon a 

 branch Is given oft which is inserted independently on to the leg farther down ; 

 and (3) an extensive insertion on to the fascia covering the calf of the leg. 

 (Only 1 and 3 of these insertions present in Seliomis, however.) 



' MaximUian, Prinz zu Wied, Beitr. Nat. Bras, iv, 1833, 287. Some of the Old 

 World forms, however, have downy young, so this statement may prove false. 



